The invention relates to a further development of the known cores of cylindrical shape, which are used for carrying a roll of self-adhesively coated materials in web form.
Such winding cores are generally of cylindrical, in other words circularly round shape. Typical embodiments comprise single or double walled plastic cores or else such cores consisting of paperboard. The internal diameters of adhesive-tape winding cores are usually adapted to the processing equipment of the rolls of self-adhesive tape containing them. Typical internal diameters are, for example, 1 inch, 1.5 inches, 50 mm or 3 inches. The thickness, shape and internal diameter of the winding cores depend, inter alia, on the requirements to be met in producing and processing the individual rolls. The widths of ready-made rolls of self-adhesive tape are typically in the range of just a few mm up to about 200 mm. The width of the winding cores respectively used usually corresponds to the width of the adhesive tape wound up onto them.
Non-cylindrical shapes of winding core are used for special self-adhesive tapes. For example, U.S. Pat. No. 5,269,421 (xe2x80x9cPackage for PSA tape has thin two-ply core with length of PS tape wound around it in layersxe2x80x9d) describes a flat, planar two-ply rectangular core, around which an adhesive tape is wound. One advantage of the adhesive tape wound onto the rectangular core is its space-saving (flat) made-up form.
Because of their round shape, cylindrical winding cores offer numerous advantages over non-round geometries for the winding and splitting process in the processing of the master rolls of adhesive tape (jumbos) to be separated into small rolls. In particular, during fabrication of the rolls it is easy to set constant winding forces over the entire circumference of the rolls. Corresponding advantages likewise apply in the processing of the small rolls.
An important quality criterion for rolls of self-adhesive tape is their freedom from telescoping and, in many cases, the absence of air inclusions (fish eyes) between neighbouring layers of adhesive tape. Telescoped rolls of self-adhesive tape can often no longer be processed satisfactorily, both because of the changes which have occurred in the shape and dimensions of the roll and because of the frequently encountered deformation of the adhesive film strip itself. Fish eyes are often undesired in the case of rolls of transparent adhesive tape for aesthetic reasons, since they reduce the transparency of the rolls. However, they also often cause increased unrolling noise when cutting the adhesive tape to length and uneven adhesive forces of the order of magnitude of the fish eyes occurring, hence they may also bring about technical disadvantages. Furthermore, it is often the case, for example, that, in spite of using adhesive tapes which are highly transparent in individual layers, information applied to the outside of the winding core, for example by printing onto it or inserting a printed paper, is not visible, or only to a restricted extent, because of the formation of fish eyes. Such hazy rolls additionally often give the consumers the impression of inferior quality. The production of rolls of adhesive tape which are free from telescoping and at the same time have no fish eyes is often impossible or in many cases can be accomplished only with difficulty without correspondingly complex technical precautions, such as are described, for example, in EP 0 670 277 A (xe2x80x9cMethod of making pressure sensitive adhesive tape rolls with a transparent to the core appearancexe2x80x9d). Thus, winding without fish eyes can only be achieved by means of a correspondingly high winding tension or a comparatively high contact pressure when producing small rolls. However, all the aforementioned measures increase the risk of the rolls of adhesive tape subsequently telescoping. This applies in particular to rolls of adhesive tape made up in great lengths and at the same time having a small roll width.
Known methods of reducing the tendency to telescope while at the same time increasing the winding tension (and the resultant reduction in the frequency of fish eyes) are to use winding cores of a barrel-shaped form, to use winding cores which have a slight elevation in the middle and to use slit cores, as are described, for example, in EP 0 430 548 A (xe2x80x9cCollapsible core adhesive rollsxe2x80x9d).
Among the main disadvantages of using the aforementioned cores are that
winding cores of a barrel-shaped form and those which have a slight elevation in the middle cannot be obtained in a simple way by separating ready-made product,
slit cores have a lower mechanical stability on account of the slits being introduced,
if winding cores of a barrel-shaped form or those with an elevation in the middle are used, adhesive tape from the winding close to the core is markedly deformed by the non-cylindrical core surface, which can not only cause an unsightly appearance of the unwound adhesive tape but can also cause a reduction in the technical suitability of the corresponding material.
A further possibility of reducing the tendency to telescope while at the same time increasing the winding tension is to use cores which have a smaller width than the adhesive tape wound up onto them. The disadvantage of this method is that, depending on the difference in width between the winding core and the adhesive tape, the wound-up adhesive tape may roll in, which may lead to similar disadvantages as described above.
The object of the invention was to provide a core which does not have the said disadvantages of the prior art and which is consequently able in particular to be wound largely without any fish eyes while at the same time reducing the tendency to telescope.
Accordingly, the outer contour of the core for winding self-adhesively coated materials in web form is formed by at least one substantially round, self-contained segment, the ends of which run together in an edge, with
a) the round segment being shaped convexly with respect to the axis of the core,
b) the normals to the surface of the round segment being aligned substantially orthogonally with respect to the axis of the core,
c) the edge being aligned substantially parallel with respect to the axis of the core,
and the core having a recess on the inside, so that the roll together with the core can be fitted on commercially available adhesive tape dispensers, which have a, in particular cylindrical, core holder.
In a second embodiment, the outer contour of the core for winding self-adhesively coated materials in web form is formed by at least two segments substantially in the form of portions of a circle, with
a) the segments being arranged convexly with respect to the axis of the core,
b) the normals to the surfaces of the segments being aligned orthogonally with respect to the axis of the core,
c) the edges at which the segments meet being aligned parallel with respect to the axis of the core
and the core having a recess on the inside, so that the roll together with the core can be fitted on commercially available adhesive tape dispensers, which have a, in particular cylindrical, core holder.
The outer contour of the core is advantageously formed by two to seven segments of the same shape in the form of portions of a circle, which are arranged symmetrically around the axis of the core, with
a) the segments being arranged convexly with respect to the axis of the core,
b) the normals to the surfaces of the segments being aligned orthogonally with respect to the axis of the core,
c) the edges at which the segments meet being aligned parallel with respect to the axis of the core.
If the core according to the invention is viewed from the side, the space bounded by the outer contour defines a regular lune to pentagon of arcs. Typical embodiments comprise curve shapes of equal thickness, such as, for example, those based on regular or even non-regular Reuleaux polygons.
In a particularly preferred embodiment of the core according to the invention, the outer contour is formed by three segments of the same shape in the form of portions of a circle, which are arranged symmetrically around the axis of the core, with again
a) the segments being arranged convexly with respect to the axis of the core,
b) the normals to the surfaces of the segments being aligned orthogonally with respect to the axis of the core,
c) the edges at which the segments meet being aligned parallel with respect to the axis of the core.
If the core according to the invention is viewed from the side, the space bounded by the outer contour defines a regular triangle of arcs.